Unburned fuel and other combustion products may escape past the piston of an internal combustion engine (e.g., an internal combustion engine of a vehicle) into the crankcase. The resulting gases in the crankcase, often referred to as “blowby” gases, may contribute to the formation of sludge in the engine oil supply. Further, blowby gases may excessively pressurize the crankcase, resulting in undesirable leakage of oil pan gasket and crankcase seals.
To avoid these issues, an engine may include a positive crankcase ventilation (PCV) system coupled to the intake, which serves to vent blowby gases from the crankcase to the intake. The PCV system may include a PCV valve intermediate the crankcase and the engine intake passage, to regulate the flow of blowby gases from the crankcase to the intake manifold. Such regulation may be needed because intake manifold vacuum characteristics may not match flow requirements for proper crankcase ventilation. For example, whereas blowby production may be greatest during high load engine conditions and very light during idle and light load engine conditions, intake manifold vacuum may be low during the high load conditions and high during the idle and light load engine conditions. Thus, intake manifold vacuum alone may not provide enough crankcase ventilation during high load conditions, yet too much crankcase ventilation may occur during idle and low load conditions due to the high intake manifold vacuum present in these conditions. Further, regulation of blowby gas flow in a PCV line (“PCV flow”) may be needed to ensure the air-fuel ratio in the intake manifold enables efficient engine operation. For example, if PCV flow does not vary in proportion to the regular air-fuel ratio being drawn into the intake manifold, the PCV flow may cause the air-fuel mixture drawn into the intake manifold to become too lean for efficient engine operation.
Various types of PCV valves may be used in engine PCV systems to regulate PCV flow. A typical crankcase vent valve restricts flow with a small orifice when a deep intake manifold vacuum exists, and is much less restrictive to flow (large orifice) when a shallow intake manifold vacuum exists. One standard PCV valve configuration includes a substantially conic member arranged within a valve housing, where the cone is oriented within the housing such that its tapered end faces the end of the valve housing which communicates with the intake manifold. When there is no vacuum in the intake manifold, for example during engine off conditions, a spring keeps the base of the cone seated against the end of the valve housing which communicates with the crankcase, such that the PCV valve is fully closed. Although the PCV valve is fully closed, an orifice running through the length of the cone allows a fixed amount of PCV flow to be metered through the PCV valve. In contrast, when there is a high level of vacuum in the intake manifold, for example under engine idle or deceleration conditions, the cone moves upward within the valve housing towards the intake manifold end of the valve housing due to the slight increase in intake manifold vacuum. At this time, the PCV valve is substantially closed, and PCV flow moves through a small annular opening between the cone and the valve housing. Because only minimal blowby gases may be present during engine idle or deceleration conditions, the small annular opening may be adequate for crankcase ventilation. When intake manifold vacuum is at a lower level, for example during part-throttle operation, the cone moves closer to the crankcase end of the valve housing, and PCV flow moves through a larger annular opening between the cone and the valve housing. At this time, the PCV valve is partially open. During part-throttle operation, there may be an increased amount of blowby gases present relative to engine idle or deceleration conditions, and thus the larger annular opening may be appropriate for crankcase ventilation. Finally, a further decrease in intake manifold vacuum (while intake manifold vacuum is still greater than zero), for example during high load conditions, moves the cone even closer to the crankcase end of the valve housing, and PCV flow moves through an even larger annular opening between the cone and the valve housing. At this time, the PCV valve is considered to be fully open, such that PCV flow through the valve is maximized. The fully open state of the PCV valve is well-suited to high load conditions, since during these conditions there may be an increased amount of blowby gases. In this way, the opening state of the PCV valve is influenced by manifold vacuum, and the flow rate of the PCV valve is proportionate to manifold vacuum. The minimum flow rate of the PCV valve is determined by the dimensions of the orifice in the conic member, as PCV flow is metered through the orifice when the PCV valve is in the fully closed position. During conditions where intake manifold pressure exceeds crankcase pressure, PCV flow may move through the valve backwards (as “PCV backflow”), towards the crankcase. PCV systems may or may not be configured to prevent such operation, as the minimal amount of PCV backflow through the orifice in the cone may or may not pose problems for engine operation.
In addition to a PCV valve, an aspirator may be included in a PCV line to generate vacuum via PCV flow. Using crankcase gases as the motive flow for an aspirator may be advantageous in that it avoids the problem of saturating engine throttle control during warm idle conditions with low front end accessory drive loads. One example approach for directing a motive flow of crankcase gases through an aspirator to generate vacuum is shown in US 2011/0132311. In one embodiment, a PCV system is in communication with an intake manifold via an aspirator. An entraining inlet of the aspirator is in communication with a vacuum reservoir. Further, a passive control valve is arranged intermediate the PCV system and the intake manifold to limit communication from the intake manifold to the PCV system. The passive control valve is described as a having a similar flow characteristic to a PCV valve. Crankcase gases vented to the intake manifold first flow through the passive control valve, then through a motive inlet of the aspirator (drawing air from the entraining inlet), and finally leave the aspirator via an outlet. In this way, air and crankcase gases may be used to generate vacuum during positive crankcase ventilation.
The inventors herein have recognized that both vacuum generation and PCV flow regulation may be accomplished via a single component. In one example, the inventors herein have conceived of an aspirator that functions as both a PCV valve and a source of vacuum when configured in the PCV system described herein. A PCV system equipped with such an aspirator may advantageously accomplish vacuum generation and PCV flow regulation by way of a single component. Use of this multi-functioning aspirator may reduce manufacturing and installation costs and simplify control of the PCV system, while also achieving the advantages associated with the use of blowby gases for vacuum generation. Further, as this aspirator may be the only PCV valve in the system in some examples, PCV flow energy that would otherwise be expended across a PCV valve orifice may be harnessed for vacuum generation under some conditions.
One example method for an engine equipped with such an aspirator includes, in a first operating mode, at least partially opening an aspirator and flowing crankcase gases through the aspirator. The method further includes, in a second operating mode, fully closing the aspirator and metering crankcase gases through an orifice of a pintle of the aspirator. In this way, an aspirator may be controlled so as to provide appropriate PCV flow regulation and vacuum generation for a current operating mode. Via the novel inclusion of an orifice in a pintle of the aspirator, the aspirator may function as a fully closed PCV valve under some conditions, whereas under other conditions the aspirator may function as a substantially closed, partially open, or fully open PCV value while simultaneously generating vacuum via the flow of crankcase gases through the aspirator. The vacuum generated by the aspirator may advantageously be used for actuation, enabling vehicle brakes, purging a fuel canister, improving an engine start, performing a leak test, etc.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.